Opinion leadership is leadership by an active media user who interprets the meaning of media messages or content for lower-end media users. Typically the opinion leader is held in high esteem by those who accept his or her opinions. Opinion leadership comes from the theory of two-step flow of communication propounded by Paul Lazarsfeld and Elihu Katz. Significant developers of the theory have been Robert K. Merton, C. Wright Mills and Bernard Berelson. This theory is one of several models that try to explain the diffusion of innovations, ideas, or commercial products.
Merton distinguishes two types of opinion leadership: monomorphic and polymorphic. Typically, opinion leadership is viewed as a monomorphic, domain-specific measure of individual differences, that is, a person that is an opinion leader in one field may be a follower in another field. An example of a monomorphic opinion leader in the field of computer technology, might be a neighborhood computer service technician. The technician has access to far more information on this topic than the average consumer and has the requisite background to understand the information, though the same person might be a follower at another field (for example sports) and ask others for advice. In contrast, polymorphic opinion leaders are able to influence others in a broad range of domains. Variants of polymorphic opinion leadership include market mavenism, personality strength and generalized opinion leadership. So far, there is little consensus as to the degree these concept operationalize the same or simply related constructs.
In his article "The Two Step Flow of Communication" by Elihu Katz, he found opinion leaders to have more influence on people's opinions, actions, and behaviors than the media. Opinion leaders are seen to have more influence than the media for a number of reasons. Opinion leaders are seen as trustworthy and non-purposive. People do not feel they are being tricked into thinking a certain way about something from someone they know. However, the media can be seen as forcing a concept on the public and therefore less influential. While the media can act as a reinforcing agent, opinion leaders have a more changing or determining role in an individual's opinion or action.